Coated paper products, such as wax-coated corrugated cardboard boxes, are used in a variety of applications. Traditionally, wax coatings modified with polymers have found a significant use in this application. Wax coating compositions on paper products provide a barrier to moisture as well as oil and grease. For example, wax-coated corrugated cardboard can be used to make poultry boxes and other types of boxes that are used to carry and transport frozen and ice packed seafood, poultry, fruits and vegetables. A wax coating composition on these boxes not only provides rigidity and strength to these boxes but also water proofing to the boxes when they are exposed to wet and frozen food products during transportation that ultimately protects the mechanical integrity of the boxes during transportation.
For wax compositions used in coating corrugated products, it is typical to use high quality paraffin waxes with a narrow molecular weight range or narrow carbon number distribution (e.g., 95% carbon number spread), and a high n-paraffin (i.e., straight-chain paraffin) content. Rationalization of Group I base stock refining capacity around the globe has led to a declining availability of corresponding wax streams that are derived from these base stocks. However, with a reduction in available sources of wax, it has become ever more important to have the flexibility of blending different wax streams without a concomitant deterioration in product properties. However, blending of wax streams with widely different molecular weights or widely different average carbon numbers is well-known to generally have a negative effect on product properties. More specifically, for use in corrugated cardboard coatings and more specifically in saturating waxes, only high quality, narrow molecular weight cut, fully-refined paraffin waxes are preferred.
It is well-known in the art that a narrow molecular weight distribution of molecules is beneficial for several key properties, including, inter alia, improved water-proofing, hardness, and oil bleed, among others. For example, wax with a wide carbon number distribution is known to be detrimental to the quality of the wax and causes “oil bleed” (Young, F. X. “Practical Applications of Gas Chromatography in Paints and Coatings Industry,” Analysis of Paints and Related Materials: Current Techniques for Solving Coating Problems, American Society for Testing and Materials (ASTM), Philadelphia, 1992, ASTM STP 1119, p 105-124). Oil bleed is the tendency of a wax to have a slick-oily surface and is related to poor wax quality and poor water proofing. Oil bleed in a coating product may provide poor surface characteristics to the coating in terms of poor appearance and lower friction coefficient of the slick coated surface. Similarly, a narrow distribution of carbon lengths and a narrow distillation cut is necessary for production of a high quality wax having sufficient hardness, especially at higher temperatures (Meyer, G. “Interactions between chain length distributions, crystallization behavior and needle penetration of paraffin waxes,” Erdol-Erdgas-Kohle Journal, 2006, 122.Jb, 1, S.16-18). Finally, the literature has described how increasing molecular weight distribution leads to a decrease in crystal perfection of crystalline materials, which in turn is directly responsible for reduction in barrier properties and water proofing of the material.
For the same reasons, high n-paraffin content is desired in waxes that are used in water proofing applications. High n-paraffin content tends to give a higher percentage of crystalline phase in the material, which in turn is responsible for good barrier properties of the material among other desirable characteristics. It is for this reason that synthetic waxes are desired to be made with narrow molecular weight distributions.
The hardness of the wax coating is also important in corrugated box coatings because harder wax coatings translate into a harder box which gives the box greater ‘dry strength’, which is needed for greater stacking strength. Stacking strength is required for such corrugated boxes because they are used to pack and transport heavy loads for fruits, meat and vegetables over long distances. In particular, the ability of the wax to maintain its stacking strength in warmer temperatures is also an important characteristic, since often food packaging is done in warmer climates. For this attribute, the ability of the wax to maintain its hardness at higher temperatures is highly desirable.
Several studies have attributed improved barrier properties of polymeric materials, in particular high density polyethylene, to a narrow molecular weight distribution of the polymer. Since the molecular architecture and crystallization behavior of polyethylene is similar to a paraffin wax molecule, the effect of molecular weight distribution on barrier properties of the material is expected to be similar by inference.
Competing with the ongoing need for wax materials, including those suitable for use in coating cellulosic materials, is the fact that the wax obtained from Group I refining process, which includes high-quality and mid and low carbon number paraffin waxes, are more and more frequently consumed for the production of lubricants. Moreover, lower quality paraffin waxes are also recycled and further processed for further lubricant production. As such, there exists in the art a need for the wax materials that demonstrate properties suitable for industrial use, e.g., coatings for cellulosic materials, candles, writing implements, etc. but that can be produced with refinery wax streams that have better long term availability such as higher carbon number paraffins.